1. Field of the Invention
The present invention relates to a method and device for selecting a method from a set of methods of transcoding digital multimedia data, the data being liable to be transferred between at least two communication apparatuses via a communication network.
2. Related Art
Technological advances in digital communication apparatuses such as television sets, pocket microcomputers, conventional microcomputers or any other miniaturized apparatus are such that, in future years, it will very probably be possible to exchange data of a multimedia type and, for example, audio and/or video between these different apparatuses.
Market studies show, moreover, that users are ready to purchase such communication apparatuses provided that the price is not too excessive and, in particular, that the services rendered are of good quality.
Following the identification of this new market, many studies have been carried out concerning the miniaturization of electronic components, so as to obtain apparatuses with high memory and computational capacities within the smallest possible volume.
In addition, many standardization bodies have produced standards for unifying data exchanges between these apparatuses with different characteristics. These standards, such as those of the IEEE 802 family, allow both the implementation and the management of the transfer of data via a particular network.
IEEE 802.11 and its European counterpart HYPERLAN are dedicated to wireless local area networks. These are being particularly studied at the present time since they are broad-band networks making it possible to transmit audio and/or video data between two machines which are geographically close.
These standards are therefore particularly adapted for developing wireless local area networks within dwellings.
The technical solutions currently being studied in the context of the above mentioned standards applied to home area networks permit wireless transmission of digital data either between a so-called server machine and a so-called client machine (point to point transmission), or between the server and several clients (multipoint communication).
In this environment, the data are stored on the server, which centralizes all the communications with the client or clients. This server can also serve as a gateway with the outside world (Internet, television, camcorder etc).
It should be noted that home area networks can be of a heterogeneous nature, that is to say they can, for example, consist partly of wireless connections and partly of cabled connections.
Though many projects are studying the implementation of services around interactive television and the exchange of information on the Internet, few of them are dealing with the problems related to the use of home area networks, namely the production of solutions for obtaining an acceptable service quality.
In this connection, it should be noted that the conveyance of data through a local area network is not a service which is easy to implement.
A communication system is known from the article “Transcoding Internet Content for Heterogeneous client devices” by J. Smith, R. Mohan, C-S. Li, Proc Int. Conf on circuits and Syst. (ISCAS), May 1998, which provides for the dynamic adaptation of the content of video data to be transmitted to a communication apparatus, to the characteristics of the apparatus and to the resources of the network.
To achieve this, a method is proposed of selecting a method of transcoding which will be adapted to the category of device and to the above-mentioned characteristics of that device and of the network.
More particularly, this method of selection searches among the methods of transcoding which are adapted to the device and to the above-mentioned characteristics for the method for which a maximum fidelity value is obtained.
It should be noted that the measurement of fidelity is representative of the impact of the transcoding method.
A method of selecting a transcoding method from a set of transcoding methods is also known from the article entitled “Modeling Quality Adaptation Capabilities of Audio-Visual Data”, H. Kosch, L. Böszörményi and H. Hellwagner, Institute of information technology, University Klagenfurt, Austria, Jul. 2001.
In that article, it is proposed to classify the transcoding methods on a quality scale graduated from 0 to 1, 1 representing a perfect quality of restoration of the data while 0 signifies that the transcoded multimedia data are very little representative of the data before transcoding.
To evaluate the quality induced by a transcoding method, it is for example possible to perform, for all the transcoding methods considered, firstly a transcoding according to the method tested, then a decoding and a quality measurement.
However, this approach is costly in terms of calculation and memory space necessary.